Evalscript for the mapping of flood on 2023.10 in Maoming, Guangdong., PRC

evalscript_for_maoming_flood.js

//VERSION=3
// This is a simple adoption from Sentinel-hub use case from [https://custom-scripts.sentinel-hub.com/sentinel-1/flood_mapping/]
// To share a long evalscript, we need a public url. Github Gist's raw url is nice way.
var beforeflood_date = "2023-10-12"; var duringflood_date = "2023-10-24";
function setup() {
  return {
    input: [{
      bands: [
        "VV"
      ]
    }],
    output: { bands: 3 },
    mosaicking: "ORBIT"
  }
}


function filterScenes (scenes) {  
return scenes.filter(function (scene) {
// set dates for before-and-during flood analysis
var allowedDates = [beforeflood_date,duringflood_date]; 
var sceneDateStr = dateformat(scene.date);
if (allowedDates.indexOf(sceneDateStr)!= -1) return true;
else return false;
  });
}

// Flood mapping
function calcFM(sample) {
  var outvv = sample.VV;
  return [1.5*outvv];
}

function dateformat(d){  
  var dd = d.getDate();
  var mm = d.getMonth()+1;
  var yyyy = d.getFullYear();
  if(dd<10){dd='0'+dd}
  if(mm<10){mm='0'+mm}
  var isodate = yyyy+'-'+mm+'-'+dd;
  return isodate;
}

function evaluatePixel(samples,scenes) {  
  var outbe = 0;
  var outdu = 0;  
  // before-flood image
  outbe = calcFM(samples[1]); 
  // during-flood image
  outdu = calcFM(samples[0]);  
  return [outbe,outdu,outdu]
 // ************************************
 // mask creation
 
//   var dout = outbe - outdu;    
//  return [dout > 0.05 ?  1 : 0]

}

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